For now, while the service is in beta, it is free, according to a blog post today from product manager Rohit Khare.

Once it’s generally available to all to use, the service will cost 40 cents per million operations of the Cloud Pub/Sub application programming interface (API) operations for the first 100 million operations. After that point, the price drops to 25 cents per million for the next 2.4 billion operations. And after that, the price goes even lower, to 5 cents per million.

Of course, data storage and movement of data from one Google data center to another will cost money, as always.

The beta availability of the tool makes Google more friendly to developers looking to easily build complex, data-rich applications. And that’s important as Amazon Web Services continues to lead the public cloud market, with Microsoft also playing a key role alongside Google.

Open-source publish-subscribe messaging tools do exist. Apache Kafka is probably the most prominent one. But it takes time to implement Kafka yourself. So this tool could come in handy for certain programmers.

Cloud Pub/Sub does have quotas. For instance, requests for publishing data — and individual messages — are capped at 10MB. See the full list of quotas for more detail.

That’s why we’re making the beta release of Google Cloud Pub/Sub available today, as a way to connect applications and services, whether they're hosted on Google Cloud Platform or on-premises. The Google Cloud Pub/Sub API provides:

Scale: offering all customers, by default, up to 10,000 topics and 10,000 messages per second